1. Field of the Invention
The present invention relates to a system and method for providing a digital In-Flight Entertainment (IFE) system in a vehicle, such as an aircraft, that is capable of presenting a video program and associated audio in a synchronized manner to a large number of individual video monitors and speakers. More particularly, the present invention relates to a system and method for achieving synchronized playback of a video program and associated audio across a large population of video and audio playback devices in an IFE system.
2. Description of the Related Art
IFE systems generally have used analog distribution technology to distribute broadcast video material, and either analog or Pulse-Code Modulation (PCM) digital for audio material. Typically, video programs originate from a single source and are distributed, through RF modulation or baseband distribution technologies, throughout the aircraft. When the video programs are distributed as analog signals, the delay from the source to the presentation device, such as a video player or overhead monitor, is very small and usually within microseconds. It addition, analog video is presented essentially as it is received by the display device. Therefore, if a baseband or RF modulated signal is distributed to all video players and overhead monitors, these presentation devices are typically synchronized to within microseconds.
In IFE systems using PCM digital distribution, the audio material is sampled at a rate consistent with the digital distribution system. Each sample of the audio is transmitted over a dedicated digital distribution system. Many systems use a Time Division Multiplex (TDM) scheme for combining multiple audio programs into a multiplexed digital data stream. The audio player identifies the time slot(s) that are to be used, extracts the samples from the desired time slot(s) and convert the sample back into an analog signal. By transmitting the audio signal sample-by-sample and by using a dedicating distribution network for this purpose, the audio is presented approximately one sample-time delayed from its source.
Current systems typically use either baseband or RF modulated video distribution for programs that are simultaneously presented to a large number of viewers. Since there is little processing performed at the presenting device and the information is distributed essentially in real time, these distribution and presentation techniques are capable of presenting video and audio that are synchronized within microseconds.
With digital content, the video and audio can be transmitted essentially un-encoded However, one video program alone would require more than 80 Mbps and one stereo audio program would require around 1.2 Mbps. This extremely high data rate requirement makes such a distribution technique impractical.
The baseband or RF modulated process currently used in aircraft can be somewhat effective in maintaining synchronization, but severely limits the quality of the video image being presented. As understood by one skilled in the art, baseband or RF modulated systems utilize the analog video standards such as PAL, SECAM, or NTSC, and these standards significantly limit the video resolution. In addition, these standards require analog signal distribution which is inconsistent with the desire to provide an all-digital entertainment network. In an aircraft IFE system, the inclusion of separate analog wiring, amplifiers and other components to support analog video/audio distribution separate from digital audio/video distribution for individual services is highly undesirable.
The added wiring can be bundled with the digital wiring to minimize the number of connectors required, and splitters and amplifiers can be combined into other boxes to minimize the cost and weight of supporting the extra functions. However, even the impact on cost, weight, power, and space can be minimized in this manner, the inclusion of both digital and analog video/audio distribution does increase the cost, weigh, and power of the system. In addition, there is a clear visual difference between video service provided by the analog distribution system when compared to that provided by the digital distribution system.
An example of a technique for synchronizing audio and video signals is set forth in U.S. Pat. No. 6,122,668.